Conventionally, an air intake apparatus where a surge tank and an air intake passage are constituted by plural pieces is known. Such air intake apparatus is disclosed, for example, in JP 2012-251518A.
JP2012-251518A discloses a three-piece construction including an upper piece positioned upward, a middle piece positioned midway, and a lower piece positioned downward. In the air intake apparatus, a downstream portion of the air intake passage is constituted by the upper piece and the middle piece. A surge tank and an upstream portion of the air intake passage are constituted by the middle piece and the lower piece. The air intake passage is communicated with the surge tank at the upstream side and is connected to an air intake port of an engine via a flange portion that is provided at an end portion of the downstream portion.
In JP2012-251518A, the flange portion is integrally formed at the middle piece. In addition, the pieces of the air intake apparatus are made of resin and are joined to one another by a vibration welding. That is, a lower end surface (welding line) of an upper wall portion of the middle piece and an upper end surface (welding line) of a lower wall portion of the lower piece are vibration-welded to thereby constitute a side wall of the surge tank.
In the vibration welding, it is necessary to slidaly move (vibrate) joint portions of members that are joined to each other. A space for vibration is thus required in the vicinity of the joint portions. Accordingly, in the aforementioned air intake apparatus of JP2012-251518A, the side wall of the surge tank constituted by the upper wall portion of the middle piece and the lower wall portion of the lower piece, and a side wall of the downstream portion (downstream side end portion) of the air intake passage of the middle piece at which the flange portion is provided are formed to be spaced away from each other at an interval for joining.